Method, terminal, and system for cell reselection

ABSTRACT

A method and terminal are disclosed for cell reselection. In the disclosure, the terminal obtains a dedicated priority list and a valid time of the dedicates priority list for cell reselection from a first communication system, such as a Long Term Evolution (LTE) system, when the terminal is in a cell of the fists communication system. In case that the terminal camps on a cell of a second communication system, such as a non-LTE system (for example, a UMTS system), and before the valid time expire, the terminal performs cell reselection using the dedicated priority list.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/030,570, filed on Jul. 9, 2018, which is a continuation of U.S.patent application Ser. No. 15/005,852, filed on Jan. 25, 2016, andissued on Aug. 14, 2018 as U.S. Pat. No. 10,051,540, which is acontinuation of U.S. patent application Ser. No. 14/671,842, filed onMar. 27, 2015, and issued on Jan. 26, 2016 as U.S. Pat. No. 9,247,493,which is a is a continuation of U.S. patent application Ser. No.14/135,045, filed on Dec. 19, 2013 and issued on Mar. 31, 2015 as U.S.Pat. No. 8,996,003, which is a continuation of U.S. patent applicationSer. No. 13/672,494, filed on Nov. 8, 2012 and issued on Jan. 28, 2014as U.S. Pat. No. 8,639,246, which is a continuation of U.S. patentapplication Ser. No. 12/902,933, filed on Oct. 12, 2010 and issued onApr. 2, 2013 as U.S. Pat. No. 8,412,197, which in turn is a continuationof International Patent Application No. PCT/CN2009/071194, filed on Apr.8, 2009. The International Patent Application claims priority to ChinesePatent Application No. 200810091957.6, filed on Apr. 9, 2008. Theaforementioned patent applications and patents are hereby incorporatedby reference in their entireties.

This application is related to U.S. patent application Ser. No.12/955,392, filed on Nov. 29, 2010, and issued on Oct. 18, 2011 as U.S.Pat. No. 8,041,355, and also related to U.S. patent application Ser. No.13/270,089, filed on Oct. 10, 2011, and issued on May 22, 2012 as U.S.Pat. No. 8,185,111, both of which are continuations of U.S. patentapplication Ser. No. 12/902,933, filed on Oct. 12, 2010 and issued onApr. 2, 2013 as U.S. Pat. No. 8,412,197.

FIELD OF THE INVENTION

Embodiments of the present invention relate to a field of mobilecommunications, and more particularly, to a method, terminal, and systemfor cell reselection.

BACKGROUND

With developments in the mobile communication field, various mobilecommunication systems have emerged, for example, a Global System forMobile Communication (GSM), an Enhanced Data for GSM Evolution (EDGE)system, a GSM/EDGE Radio Access Network (GERAN) system, a Wideband CodeDivision Multiple Access (WCDMA) system, a Code Division Multiple Access(CDMA) system, a Code Division Multiple Access 2000 (CDMA2000) system, aTime Division-Synchronous CDMA (TD-SCDMA) system, a Long Term Evolution(LTE) system under development and establishment, a WorldInteroperability for Microwave Access (WIMAX) system, etc. The WCDMAsystem may also be referred to as Universal Mobile TelecommunicationsSystem (UMTS). Due to the emergence of the various systems, when aterminal performs cell reselection during movement, there may be severalfrequencies available for selection in the system, and there may be manycells of several systems available for selection. Therefore, it becomesan important issue as to how the terminal reselects a suitable cell andhow to reduce measurements to save power energy.

In the current LTE system, considering that the terminal should reducemeasurement overhead to save power energy, when performing cellreselection, the terminal will decide a cell on which the terminal is tocamp according to the priority. Specifically, the terminal will firstmeasure a frequency or system having a higher priority. If a cell of thefrequency or system having a higher priority meets the cell reselectioncriterion, the cell will be reselected; otherwise, a cell having a lowerpriority will be measured. If a terminal camps on a cell having a lowerpriority, a cell having a higher priority might be measuredperiodically. The priority-based cell reselection method may reduce themeasurements by the terminal and save power energy. Meanwhile, a goodpriority setting may lead to load balance.

In the existing technical solutions, the terminal performs cellreselection by using a dedicated priority list established by thenon-LTE mobile communication system. The Access Network (AN) node or theCore Network (CN) node has to add more signaling for establishment ofthe dedicated priorities, which leads to higher costs for networkupgrade.

SUMMARY

To solve the problems in the conventional art that establishment of thededicated priority list by the non-LTE system causes too much increasedsignaling and too high costs for network upgrade, an embodiment of theinvention provides a method, terminal, and system for cell reselection.

An embodiment of the invention provides a method for cell reselection,including: a terminal obtains a dedicated priority list and a valid timeof the dedicated priority list from a first system, and the terminalperforms a cell reselection according to the dedicated priority list andthe valid time of the dedicated priority list, when the terminal campson a cell of a second system.

An embodiment of the invention provides a terminal, including:

a first obtaining unit configured to obtain a dedicated priority listand a valid time of the dedicated priority list from a first system; afirst storage configured to store the dedicated priority list; and afirst processing unit configured to perform a cell reselection accordingto the dedicated priority list and the valid time of the dedicatedpriority list stored in the first storage when the terminal camps on asecond system.

An embodiment of the invention provides a system, including anetwork-side device and a terminal as provided in any embodiment of theinvention, where the network-side device is configured to send thededicated priority list.

In an example where the first system is an LTE system and the secondsystem is a non-LTE system, the terminal according to the embodiments ofthe invention may perform cell reselection by using the dedicatedpriority list obtained from the LTE system, so as to free the non-LTEsystem from establishing the dedicated priority list. Problems in theconventional art that establishment of the dedicated priority list bythe non-LTE system causes too much increased signaling and too highcosts for network upgrade, are solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method provided in an embodiment of thepresent invention;

FIG. 2 is a flow chart of a method provided in embodiment 1 of thepresent invention; and

FIG. 3 is a schematic diagram of a terminal provided in embodiment 6 ofthe present invention.

DETAILED DESCRIPTION

To further clarify the objects, the technical solutions, and theadvantages of the present invention, detailed descriptions are givenbelow to the implementation of the present invention with reference tothe accompanying drawings.

Referring to FIG. 1, a cell reselection method provided in an embodimentof the present invention includes the following steps.

In step 001, a terminal obtains a dedicated priority list from a firstsystem.

In step 002, the terminal performs a cell reselection according to thededicated priority list when the terminal camps on a cell of a secondsystem.

In the above embodiment of the invention, the terminal performs the cellreselection by using the dedicated priority list obtained from the firstsystem. In this way, there is no need for the second system to establishthe dedicated priority list.

Further, the first system may be an LTE system and the second system maybe a non-LTE system in an embodiment of the invention. Accordingly,problems in the conventional art that establishment of the dedicatedpriority list by the non-LTE system causes too much increased signalingand too high costs for network upgrade, are solved.

Further, the terminal in this embodiment may also obtain the valid timeof the dedicated priority list from the LTE system. Before the validtime expires, the terminal camping on a cell of the non-LTE system mayperform cell reselection according to the dedicated priority list. Afterthe valid time expires, the dedicated priority list is invalid. Then,the terminal may perform cell reselection according to a public prioritylist, or perform cell reselection according to a result measured inaccordance with a cell signal quality criterion, or search for a cell ofthe LTE system.

Further, the above public priority list may be obtained by the terminalfrom the LTE system or the non-LTE system. Optionally, the terminal mayprocess the public priority list according to an indication which isused to notify the terminal that the non-LTE system will not deliver thepublic priority list and/or notify the terminal to store the publicpriority list obtained from the LTE system.

Further, the terminal may also perform other processes related to cellreselection according to an indication from the non-LTE system. Theindication may notify the terminal of any one of (or the combination of)the following: (1) searching for a cell of the LTE system when thededicated priority list is invalid; (2) searching for a cell of the LTEsystem when the terminal does not store the dedicated priority list andthe public priority list; and (3) performing cell reselection accordingto a result measured in accordance with a cell signal quality criterionwhen the terminal does not store the dedicated priority list and thepublic priority list.

In an embodiment of the invention, if no dedicated priority list isdelivered to the terminal from a UMTS or GERAN system, the terminal mayuse the dedicated priority list obtained from LTE system and the timelength of the valid time of the dedicated priority list. The terminalmay use a public priority list delivered from the UMTS or GERAN system.Alternatively, if no public priority list is delivered from the UMTS orGERAN system, or a public priority list delivered from the UMTS or GERANsystem is not received, a public priority list obtained from the LTEsystem may be used. When the terminal stores both the dedicated prioritylist and the public priority list, the dedicated priority list may beused for cell reselection. When the terminal has no dedicated prioritylist, the public priority list may be used for cell reselection.

It should be noted that, UMTS and GERAN systems are taken as an exampleto describe the embodiments of the invention for ease of illustration.The embodiments of the invention are equally applicable to other non-LTEsystems, for example, the GSM system, the WCDMA system, the CDMA system,the TD-SCDMA system, or the WIMAX system. Additionally, signal qualityof cell reselection, which is one of the performance measurementsrelated to the cell reselection procedure, is taken as an example forillustration in an embodiment of the invention.

A priority in the priority list may refer to the priority level of afrequency or a Radio Access Technology (RAT). It may also refer to thepriority level of a Frequency Band in GERAN. The priority list mayinclude the priority levels of the frequency of the serving cell, itsadjacent frequencies, and the neighboring systems, as well as thepriority level assigned for each frequency or Frequency Band of aneighboring system.

In the following embodiments 1-4, the cell reselection procedure isdescribed in a case where the terminal is idle, that is, the terminal ispower-on but not activated.

Embodiment 1

In this embodiment, the terminal camps on a cell of an LTE system. TheLTE system may deliver a dedicated priority list via a dedicatedsignaling and deliver a public priority list in system broadcastinformation. An UMTS or GERAN system may deliver a public priority list.The public priority list delivered in broadcast information of the UMTSor GERAN system may indicate a priority as LTE>UMTS>GERAN. A publicpriority list may be delivered in broadcast information of the LTEsystem. Alternatively, the public priority list may be delivered via adedicated signaling (for example, a Radio Resource Control (RRC)dedicated signaling) or a Non-Stratum (NAS) message when a dedicated RRCconnection is established. The delivered public priority list mayindicate that LTE>UMTS>GERAN. It can be understood that the abovepriority lists may indicate the same or different priorities. Thededicated priority list delivered in dedicated signaling of the LTEsystem may indicate that GERAN>UMTS>LTE.

Referring to FIG. 2, a method for cell reselection according toembodiment 1 of the invention may include the following steps.

In step 101, when a terminal camps on a cell of an LTE system, theterminal obtains a dedicated priority list and a public priority listfrom the LTE network side, and stores the two priority lists.

In step 102, the terminal performs cell reselection according to theobtained dedicated priority list. Since the dedicated priority listindicates a priority as GERAN>UMTS>LTE, the terminal in the cell of theLTE system reselects and enters into a cell of a GERAN system.

Those skilled in the art will appreciate that the terminal in the cellof the LTE system will reselects and camps on the cell of the GERANsystem according to the dedicated priority list. If signal quality ofthe cell of the GERAN system does not meet the signal quality criterion,the terminal in the cell of the GERAN system performs a cell reselectionagain according to the dedicated priority list so as to reselect andenters into a cell of an UMTS system.

In step 103, the terminal obtains a public priority list from the UMTSor GERAN network side and stores the public priority list.

In step 104, the terminal in the cell of the UMTS or GERAN systemobtains an indication from the UMTS or GERAN system broadcastinformation.

The indication is delivered periodically in the system broadcastinformation from the UMTS or GERAN network side. The indicationindicates whether the public priority list delivered from the UMTS orGERAN system is usable or not. In this embodiment, for example, theindication shows that the public priority list delivered from the UMTSor GERAN system is usable.

It can be understood that the delivery of the indication in the systembroadcast information from the UMTS or GERAN network side is not limitedby whether the terminal is in the cell of the UMTS or GERAN system.

In step 105, the above indication notifies the terminal that the publicpriority list delivered from the UMTS or GERAN network side is usable.Then, the terminal deletes the public priority list obtained from theLTE system.

The above deletion of the public priority list obtained from the LTEsystem by the terminal is optional. Alternatively, the terminal maylabel the public priority list obtained from the LTE system as“unusable”, rather than deleting the list.

In step 106, before the signal quality of the current cell decreases toa certain level, the terminal in the cell of the UMTS or GERAN systemmay perform cell reselection according to the dedicated priority listobtained from the LTE system until the dedicated priority list isinvalid.

The invalidation of the dedicated priority list may be implemented bysetting a timer. In other words, a valid time of the dedicated prioritylist is set by a timer and the timer starts when the terminal obtainsthe dedicated priority list. Before the timer expires, the dedicatedpriority list is GERAN>UMTS>LTE. Thus, the terminal will attempt toreselect a cell of the LTE system only when the signal quality of thecurrent cell decreases to a certain level (for example, when it is lowerthan a preset threshold value). The valid time of the dedicated prioritylist may be delivered to the terminal by an evolved base station(eNodeB) via a RRC dedicated signaling, for example, an RRC ConnectionRelease message, or may be delivered in a Non-Access Stratum (NAS)message to the terminal by a CN node. Before the timer expires, theterminal camps on a cell which has the highest priority shown in thededicated priority list. At this time, the terminal decides whether toperform cell reselection according to signal quality of the cell. Whenthe signal quality of the cell decreases to a preset threshold, theterminal may perform cell reselection.

In step 107, when the dedicated priority list is invalid, the terminalstops using the dedicated priority list and deletes the dedicatedpriority list. The terminal uses the public priority list for cellreselection. Since the priority shown in the public priority list isLTE>UMTS>GERAN, the terminal reselects a cell of the LTE system.

In step 108 (not shown in FIG. 2), when the terminal camps on a cell ofthe LTE system, the terminal obtains a new dedicated priority list and avalid time of the new dedicated priority list from the network side viaa Tracing area (TA) update or a periodical TA update procedure.

In this embodiment, step 103 is optional. In other words, the UMTS orGERAN network side may deliver no public priority list, and the terminaluses the public priority list obtained from the LTE system.

In this embodiment, step 104 is optional. If no indication is deliveredin the UMTS or GERAN system broadcast information, the terminal and thenetwork side defaults that the UMTS or GERAN delivers the publicpriority list in the system broadcast information and the publicpriority list is usable.

In this embodiment, the terminal performs cell reselection by using thededicated priority list obtained from the LTE system and the valid timeof the dedicated priority list. This is applicable to the case in whichthe UMTS or GERAN system delivers no dedicated priority list to theterminal. When there is no dedicated priority list, the terminalperforms cell reselection by using the public priority list obtainedfrom the LTE system or delivered from the UMTS or GERAN system. In thisembodiment, the terminal uses the dedicated priority list obtained fromthe LTE system for cell reselection so that the non-LTE system may befreed from establishment of the dedicated priority list. Problems in theconventional art that establishment of the dedicated priority list bythe non-LTE system causes too much increased signaling and too highcosts for network upgrade, are solved.

Embodiment 2

In this embodiment, a terminal camps on a cell of an UMTS or GERANsystem, and the UMTS or GERAN system delivers a public priority list.Accordingly, the terminal can only obtain the public priority list fromthe UMTS or GERAN system broadcast information and stores the publicpriority list. The terminal cannot obtain a dedicated priority list anda public priority list delivered from the LTE system. The publicpriority list delivered from the UMTS or GERAN system broadcastinformation indicates that the priority is LTE>UMTS>GERAN. When theterminal enters into a cell of the LTE system, the LTE system delivers apublic priority list in the system broadcast information. The publicpriority list delivered in the LTE system broadcast informationindicates that the priority is LTE>UMTS>GERAN. The dedicated prioritylist delivered in the LTE system via a dedicated signaling, thededicated priority list indicates that the priority is GERAN>UMTS>LTE.

When the terminal camps on a cell of the UMTS or GERAN system, theterminal performs cell selection after power-on or move back from anon-coverage area to a coverage area. For example, the terminal camps ona cell of the UMTS or GERAN system before power-off. When the terminalis power-off, information about the cell of the UMTS or GERAN system isstored. When the terminal is power-on, the terminal searches for a cellof the UMTS or GERAN system. When there is a suitable cell in the UMTSor GERAN system, the terminal camps on the suitable cell. Alternatively,when the terminal stores no information about the cell of the UMTS orGERAN system, or when the terminal moves back from a non-coverage areato a coverage area, the terminal selects and camps on a cell of the UMTSor GERAN system after power-on.

A method for cell reselection in embodiment 2 of the invention mayinclude the following steps.

In step 201, a terminal obtains a public priority list from an UMTS orGERAN system broadcast information and stores the priority list.

In step 202, the terminal performs cell reselection according to theabove public priority list. Since the priority of the public prioritylist is LTE>UMTS>GERAN, the terminal reselects a cell of an LTE system.

In step 203, when the terminal enters into a cell of the LTE system, theterminal obtains a dedicated priority list from the network side of theLTE system via a TA update procedure or a periodical TA update procedureor a traffic setup and release procedure. After obtaining the dedicatedpriority list, the terminal reselects a cell of the GERAN systemaccording to the dedicated priority list.

Those skilled in the art can understand that the subsequent steps204-208 of this embodiment are similar to steps 104-108 of embodiment 1after the terminal enters into the cell of the GERAN system. Thus, norepeated description is made here. It is optional whether the UMTS orGERAN delivers an indication in the system broadcast information.

This embodiment differs from the previous embodiment in that: when theterminal camps on the cell of the UMTS or GERAN system; the UMTS orGERAN system delivers no dedicated priority list to the terminal, butmay deliver a public priority list to the terminal; the terminal may usethe public priority list to reselect a cell of the LTE system; thededicated priority list delivered from the LTE system may be obtained,and cell reselection may be performed once more.

In this embodiment, the terminal performs cell reselection by using thededicated priority list obtained from the LTE system and the valid timeof the dedicated priority list. This is applicable to the case in whichthe UMTS or GERAN system delivers no dedicated priority list to theterminal. When there is no dedicated priority list, the terminalperforms cell reselection by using the public priority list obtainedfrom the LTE system or delivered from the UMTS or GERAN system. Due tothe fact that the terminal performs cell reselection by using thededicated priority list obtained from the LTE, the non-LTE system may befreed from establishment of the dedicated priority list. Problems in theconventional art that establishment of the dedicated priority list bythe non-LTE system causes too much increased signaling and too highcosts for network upgrade, are solved.

Embodiment 3

In this embodiment, a terminal camps on a cell of an LTE system. The LTEsystem may deliver a dedicated priority list via a dedicated signalingand deliver a public priority list in system broadcast information. AnUMTS or GERAN system delivers no public priority list. The publicpriority list delivered in the LTE system broadcast information mayindicate a priority as LTE>UMTS>GERAN, and the dedicated priority listdeliver via the LTE dedicated signaling may indicate a priority asGERAN>UMTS>LTE.

A method for cell reselection in this embodiment may include thefollowing steps.

In step 301, a terminal camps on a cell of the LTE system. The terminalhas obtained a dedicated priority list and a public priority list fromthe LTE network side, and has stored the two priority lists.

In step 302, after obtaining the priority lists, the terminal performscell reselection according to the dedicated priority list. Since thededicated priority list indicates a priority as GERAN>UMTS>LTE, theterminal in the cell of the LTE system reselect and enters into a cellof a GERAN system.

In step 303, the terminal obtains an indication from the UMTS or GERANsystem broadcast information.

The above indication is delivered from the UMTS or GERAN network side tothe terminal in the system broadcast information, used to indicate thatthe UMTS or GERAN system delivers no public priority list. Then, theterminal retains the public priority list obtained from the LTE.

In step 304, the above indication notifies the terminal that the UMTS orGERAN will not deliver any usable public priority list, and the terminalretains the public priority list obtained from the LTE.

The indication is not limited to the above contents, and may includesome extended contents as follows.

(1) The terminal is notified to perform a periodical search for a cellof the LTE system when the dedicated priority list obtained from the LTEsystem is invalid and is deleted.

(2) The terminal is notified to perform a cell reselection procedure byusing an existing cell reselection criterion when no priorityinformation is stored. In other words, the terminal uses the existingcell reselection criterion which makes measurement and comparisonaccording to a signal quality criterion.

During implementation, a bit included in the indication may be used todetermine one of the three contents included in the above indication.Alternatively, three choices may be provided at the same time via twobits included in the indication.

In the above solution, step 303 is a mandatory step. When the terminallearns from the indication that the UMTS or GERAN system will notdeliver any available public priority list and the terminal has notstored any public priority list, the terminal may perform subsequentoperations according to the extended contents of the above indication.

Steps 305-307 of this embodiment are similar to steps 106-108 ofembodiment 1, and thus no repeated description is made here.

In this embodiment, after the terminal enters into a cell of the UMTS orGERAN system, the UMTS or GERAN system will not deliver a publicpriority list. The terminal performs subsequent actions according to theindication delivered from the UMTS or GERAN system or the publicpriority list obtained from LTE system and stored at the terminal.

In this embodiment, the terminal performs cell reselection by using thededicated priority list obtained from the LTE system. Thus, the non-LTEsystem may be freed from establishment of the dedicated priority list.Problems in the conventional art that establishment of the dedicatedpriority list by the non-LTE system causes too much increased signalingand too high costs for network upgrade, are solved. Meanwhile, in thecase that the terminal receives no public priority list delivered fromthe non-LTE system, subsequent actions may be performed by using thededicated priority list obtained from the LTE system or according to thereceived indication, which improves the flexibility for cellreselection.

Embodiment 4

In this embodiment, a terminal camps on a cell of an UMTS or GERANsystem. The UMTS or GERAN system will not deliver a public prioritylist. An LTE system may deliver a dedicated priority list via adedicated signaling, and deliver a public priority list in systembroadcast information. The public priority list delivered from the LTEsystem broadcast information indicates a priority as LTE>UMTS>GERAN. Thededicated priority list delivered via the LTE dedicated signalingindicates a priority as GERAN>UMTS>LTE.

A method for cell reselection in this embodiment may include thefollowing steps.

In step 401, a terminal camps on a cell of an UMTS or GERAN system, butthe terminal has not obtained a dedicated priority list and a publicpriority list.

In step 402, the network side of the UMTS or GERAN system delivers anindication to the terminal in system broadcast information.

In step 403, the terminal in the cell of the UMTS or GERAN systemobtains the indication from the system broadcast information.

In step 404, the above indication notifies the terminal that the cell ofthe UMTS or GERAN system has not delivered a public priority list.

Or, the indication notifies the terminal to perform a periodical searchfor a cell of an LTE system when the dedicated priority list is invalid.

Or, the indication notifies the terminal to perform a cell reselectionprocedure by using an existing cell reselection criterion when nopriority information is stored.

In step 405, the terminal reselects and enters to a cell of an LTEsystem.

The terminal may reselect a cell of the LTE system by performing aperiodical search for the cell of the LTE system. Alternatively, theterminal may reselect the cell of the LTE system by performing a cellreselection procedure using the existing cell reselection criterion.

In step 406, when the terminal camps on a cell of the LTE system, theterminal obtains a dedicated priority list from the network side via aTA update procedure or a periodical TA update procedure or a trafficsetup and release procedure, and obtains a public priority list from thenetwork side via system broadcast information. After obtaining thepriority list, the terminal performs cell reselection according to thededicated priority list. Since the dedicated priority list isGERAN>UMTS>LTE, the terminal in the cell of the LTE system reselects andenters into a cell of the UMTS or GERAN system.

The steps subsequent to step 406 are similar to those steps inembodiment 3 performed after the terminal in the cell of the LTE systemreselects and enters into a cell of the UMTS or GERAN system. Thus, norepeated description is made here.

This embodiment differs from embodiment 3 in that the terminal camps ona cell of the UMTS or GERAN system, the UMTS or GERAN system will notdeliver a public priority list, and the terminal performs subsequentactions according to the indication delivered from the UMTS or GERANsystem.

In this embodiment, the terminal performs cell reselection by using thededicated priority list obtained from the LTE system. Thus, the non-LTEsystem may be freed from establishment of the dedicated priority list.Problems in the conventional art that establishment of the dedicatedpriority list by the non-LTE system causes too much increased signalingand too high costs for network upgrade, are solved. Meanwhile, in thecase that the terminal receives no public priority list delivered fromthe non-LTE system, subsequent actions may be performed by using thededicated priority list obtained from the LTE system or according to thereceived indication, which improves the flexibility for cellreselection.

In the following embodiments of the cell reselection procedure, forexample, the terminal is activated, that is, the terminal is in theconnected state. The activated terminal switches to a new cell via thecell reselection procedure.

Embodiment 5

In this embodiment, a terminal camps on a cell of an LTE system and theterminal is activated. The activated terminal switches from the cell ofthe LTE system to a cell of an UMTS or GERAN system. The LTE systemdelivers a dedicated priority list via a dedicated signaling, anddelivers a public priority list in system broadcast information. TheUMTS or GERAN system delivers a public priority list. The publicpriority list delivered in the UMTS or GERAN system broadcastinformation indicates a priority as LTE>UMTS>GERAN. The public prioritylist delivered in the LTE system broadcast information indicates apriority as LTE>UMTS>GERAN. The dedicated priority list delivered in theLTE dedicated signaling indicates a priority as GERAN>UMTS>LTE.

A method for cell reselection according to this embodiment includes thefollowing steps.

In step 501, a terminal activated in a cell of an LTE system obtains adedicated priority list and a public priority list from the LTE networkside, and stores the two priority lists.

During an RRC connection setup procedure, the terminal obtains thededicated priority list in the following steps. When the terminalperforms the RRC connection setup procedure with an eNodeB, upon entryinto the RRC connection state, the terminal obtains a new dedicatedpriority list and releases the old dedicated priority list at the sametime.

Alternatively, the terminal may not release the current dedicatedpriority list after the RRC connection established. Instead, the currentdedicated priority list is overlaid with a new dedicated priority listin an RRC connection release message.

In step 502, the terminal switches from the cell of the LTE system to acell of the UMTS or GERAN system, and releases the RRC connection in thecell of the UMTS or GERAN system.

After the terminal enters into the cell of the UMTS or GERAN system,steps 503-508 to be performed are similar to steps 103-108 of embodiment1, and thus no repeated description is made here.

In the technical solution according to this embodiment, an activatedterminal performs a cell reselection/switch from a cell of the LTEsystem to a cell of the UMTS or GERAN system. The terminal obtains adedicated priority list during the RRC connection setup procedure. Or,during the RRC connection setup procedure, the current dedicatedpriority list is not released, and the current dedicated priority listis overlaid with a new dedicated priority list in the RRC connectionrelease message. The problem in the conventional art that the olddedicated priority list is deleted before the terminal obtains a newdedicated priority list, is solved. Meanwhile, in this embodiment, theterminal performs cell reselection by using the dedicated priority listobtained from the LTE system, which may free the non-LTE system fromestablishment of the dedicated priority list. Problems in theconventional art that establishment of the dedicated priority list bythe non-LTE system causes too much increased signaling and too highcosts for network upgrade, are solved.

Embodiment 6

Referring to FIG. 3, this embodiment provides a terminal capable ofperforming the methods provided in the embodiments of the invention. Theterminal includes:

a first obtaining unit 61 configured to obtain a dedicated priority listfrom a first system;

a first storage 62 configured to store the dedicated priority listobtained by the first obtaining unit 61; and

a first processing unit 63 configured to perform cell reselectionaccording to the dedicated priority list stored in the first storage 62when the terminal camps on a second system.

Furthermore, the terminal may also includes:

a second obtaining unit configured to obtain a public priority list fromthe first system and/or the second system; a second storage configuredto store the public priority list obtained by the second obtaining unit;and a second processing unit configured to perform cell reselectionaccording to the public priority list stored in the second storage whenthe terminal camps on the second system and the first storage 62 doesnot store a valid dedicated priority list.

Furthermore, the terminal may also includes:

a third obtaining unit configured to obtain an indication from thesecond system;

a third storage configured to store the indication; and

a third processing unit configured to operate according to theindication stored in the third storage.

Further, the first system may be an LTE system and the second system maybe a non-LTE system in this embodiment.

Furthermore, an embodiment of the invention provides a system, includinga network-side device and a terminal as provided in the above embodiment6, the network-side device configured to send the dedicated prioritylist.

Embodiment 7

This embodiment provides a system, including a network-side device and aterminal.

The network-side device is configured to deliver an indication to theterminal, where the indication is used to notify the terminal that thenon-LTE system on which the terminal camps will not deliver the publicpriority list, or notify the terminal to store the public priority listobtained from the LTE system, or notify the terminal to search for acell of the LTE system when the dedicated priority list stored in theterminal is invalid or search for a cell of the LTE system or performcell reselection according to a result measured in accordance with acell signal quality criterion when the terminal does not store thededicated priority list and the public priority list.

The terminal is configured to receive an indication from thenetwork-side device and perform cell reselection according to theindication.

Embodiment 8

This embodiment provides a system, including a network-side device and aterminal.

The network-side device is within an LTE system, including a firsttransmission unit configured to transmit a dedicated priority list.

The terminal includes a first storage configured to receive and storethe dedicated priority list, and a first processing unit configured toperform cell reselection according to the dedicated priority list whenthe terminal camps on a cell of a non-LTE system.

In the above embodiments 6-8, the non-LTE system may be a GSM system, anEDGE system, a WCDMA system, a CDMA system, a TD-SCDMA system, or aWIMAX system.

In the above embodiments 6-8, the terminal performs cell reselection byusing a dedicated priority list obtained from the first system (forexample, an LTE system). Thus, the second system (for example, a non-LTEsystem) may be freed from establishing the dedicated priority list.Problems in the conventional art that establishment of the dedicatedpriority list by the various systems causes too much increased signalingand too high costs for network upgrade, are solved.

From the above description to the various embodiments, those skilled inthe art may clearly appreciate that the present invention may beimplemented by means of software and a necessary general-purposehardware platform. Alternatively, the present invention may beimplemented in hardware. The former case, however, is a more preferredimplementation in many cases. Based on this understanding, the technicalsolution of the present invention in its essence or the features whichmake a contribution to the conventional art may be embodied in asoftware product. The computer software product may be stored in astorage media, such as ROM/RAM, magnetic disk, optic disc, etc.,including several instructions which cause a computer device (a PC, aserver, a network device, or the like) to perform the methods accordingto the various embodiments of the present invention.

Detailed descriptions have been made above to the invention withreference to some exemplary embodiments, which are not used to limit thepresent invention. Various changes, equivalent substitutions, andimprovements within the principle of the invention are intended to fallwithin the scope of the invention.

What is claimed is:
 1. A method for cell reselection comprising:sending, by a first network device of a first system, a dedicatedpriority list and a valid time of the dedicated priority list to aterminal; obtaining, by the terminal, the dedicated priority list andthe valid time of the dedicated priority list from a first system;sending, by a second network device of a second system, a publicpriority list to the terminal and an indication indicating whether thepublic priority list from the second system is usable or not; obtaining,by the terminal, the public priority list and the indication indicatingwhether the public priority list from the second system is usable ornot; performing, by the terminal, cell reselection according to thededicated priority list, when the terminal camps on a cell of the secondsystem; and when the terminal camps on the cell of the second system,performing cell reselection according to the public priority list fromthe second system when the indication indicating the public prioritylist from the second system is usable and when the dedicated prioritylist is invalid after the valid time expires.
 2. The method according toclaim 1, wherein the first system is a Long Term Evolution (LTE) systemand the second system is a non-LTE system.
 3. The method according toclaim 1, wherein the dedicated priority list and the valid time arecarried in a dedicated signaling.
 4. The method according to claim 1,further comprising: deleting, by the terminal, the dedicated prioritylist when the valid time expires.
 5. The method according to claim 1,wherein the dedicated priority list comprises priority information ofdifferent radio access technologies (RATs).
 6. The method according toclaim 5, wherein the priority information comprises priority informationof frequencies of the different RATs.
 7. The method according to claim1, wherein the dedicated priority list comprises frequency priorityinformation of the LTE system and the non-LTE system.
 8. Acommunications system, comprising: a first network device of a firstsystem, configured to send a dedicated priority list and a valid time ofthe dedicated priority list to a terminal; a second network device of asecond system, configured to send a public priority list to the terminaland an indication indicating whether the public priority list from thesecond system is usable or not; a terminal, configured to obtain thededicated priority list and the valid time of the dedicated prioritylist from a first system, obtain the public priority list and theindication indicating whether the public priority list from the secondsystem is usable or not, perform cell reselection according to thededicated priority list, when the terminal camps on a cell of the secondsystem; and when the terminal camps on the cell of the second system,the terminal is further configured to perform cell reselection accordingto the public priority list from the second system when the indicationindicating the public priority list from the second system is usable andwhen the dedicated priority list is invalid after the valid timeexpires.
 9. The system according to claim 8, wherein the first system isa Long Term Evolution (LTE) system and the second system is a non-LTEsystem.
 10. The system according to claim 8, wherein the dedicatedpriority list and the valid time are carried in a dedicated signaling.11. The system according to claim 8, the terminal is further configuredto delete the dedicated priority list when the valid time expires. 12.The system according to claim 8, wherein the dedicated priority listcomprises priority information of different radio access technologies(RATs).
 13. The system according to claim 12, wherein the priorityinformation comprises priority information of frequencies of thedifferent RATs.
 14. The system according to claim 8, wherein thededicated priority list comprises frequency priority information of theLTE system and the non-LTE system.